The regulation of processes such as growth, gene expression, and morphogenesis in higher organisms is difficult to study due to the complex nature of interactions that go on in the context of multicellularity. The objective of the work proposed here is to develop a parallel model system using procaryotes in which the contributions of individual cells to the properties of the multicellular "organism," be it a bacterial macrofiber or a colony, can be precisely determined. The long-range goal is to eventually understand the relationships between genetic, biomechanical, and other factors that govern higher order complexity in organisms. Such relationships have broad significance in health-related sciences. The specific aims of the experiments described in this proposal lie in three areas: (i) to ascertain the means by which individual cell growth leads to the formation of complex three-dimensional, multicellular helical fibers of given hand and degree of twist, (ii) to obtain estimates of the forces produced during growth of cells from measurements of motions, and (iii) to characterize the newly discovered system of nutrient depletion gradient fields that governs gene expression at a particular time and place within colonies of Bacillus subtilis. The first two projects shall include examination of multi-strand helix formation starting from single cells, analysis of the underlying mechanics, and development of super-coiling models related to the observed geometry. Helix hand inversion and growth under artificial constraints will also be studied. Time-lapse and laser tweezer methods will be used. The gene expression project will involve a thorough examination of the patterns of gene expression during colony growth and, in macrofibers, characterization of the signalling system, analysis of the relationship between cell growth geometry and the pattern of gene expression obtained, identification and possibly purification of the signaller, and identification of the gene(s) that govern signal production and response to the signaller. Microbiological, biochemical, genetic, and molecular genetic approaches will be used in these studies.